This message is displayed when you select an inaccessible field from the field picklist when creating / editing an expression. This can happen if you do not have access to that field. This can also happen if you do not have a license for the package which includes the selected field.

When this message is displayed, ensure license, profile access, and availability of the required fields and objects, and launch the SFM Designer again.

Note that if an SFM transaction includes a deleted field, no error message is displayed.

The expressions, maps, source/target object updates, page layouts, and advanced options display a blank value where the deleted field was configured. Saving those expressions, maps, source/target object updates, page layouts, and advanced options after any updates as required will remove the deleted field from the SFM configuration.

Updates are not mandatory before saving, and depend on where the deleted field is used. For example, if it is included in a map, no update to the map is required. However, if it is included in an expression or sorting, you may have to update them before saving.

The above behavior is to ensure that deleted fields need not be undeleted or recreated to be able to access and update such SFM transactions.